VI Using the figuredescribeRam Air Turbine.Ram Air Turbine UNIT 4 BACK-UP CONVERTERS
AIMS OF THE UNIT:- tobe able to describe back-up converters
TASKS 1 Do your best to answer the brainstorming questions. 2 Read the text for general understanding. 3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian equivalents of the words. 5 Write sentences with the new vocabulary. 6 Make up exercises as in the UNIT 2page 211 (EXERCISES FOR BETTER REMEMBERING THE TOPIC). 7 Speak on the topic. Given schemes will help you to remember and understand the topic. 8 Find more information about the text and make up a project work on the topic.
1What are back-up converters? 2 What is ELMS? The requirements for ETOPS have led to the need for an additional method of back-up power supply, short of deploying the RAT that should occur in only the direst emergency. The use of back-up converters satisfies this requirement and is used on the Boeing 777. Back-up generators are driven by the same engine accessory gearbox but are quite independent of the main IDGs. The back-up generators are VF and therefore experience significant frequency variation as engine speed varies. The VF supply is fed into a back-up converter which, using the DC link technique, first converts the AC power to DC by means of rectification. The converter then synthesizes three-phase 115 VAC 400 Hz power by means of sophisticated solid-state power-switching techniques. The outcome is an alternative means of AC power generation which may power some of the aircraft AC busbars; typically the 115 VAC transfer buses in the case of the Boeing 777. In this way substantial portions of the aircraft electrical system may remain powered even though some of the more sizeable loads such as the galleys and other non-essential loads may need to be shed by the Electrical Load Management System (ELMS).
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